So, it appears that, in Western Australia, neither laptop computers, nor
desktop computers, are available, that are new, that are compatible with
Linux, and that are reasonably priced (under 1100 AUD), and that can do what
I want (including 1240x1024 graphics resolution).
Don't about Western Australia, but there are nowadays some computers you
can buy which come natively with support for GNU/Linux.
Other than Dell, I'll mention the Lemote machines (hard to get outside
of China, tho, in my experience), the Fit-PC2, the TouchBook, ...